BAGHDAD (AFP/Reuters) - Two US army helicopter pilots were killed in an accident near an airfield in northern Iraq on Sunday, the military said in a statement. The aircraft made a hard landing inside the base. There were no enemy forces present and no hostile fire was reported, the army said, without giving further details. The accident is under investigation. Meanwhile, five police officers were also killed and one was wounded when a roadside bomb exploded in a volatile northeastern area of Iraq that is claimed by Arabs and Kurds, police said. The bomb targeted a patrol of police assigned to protect power installations near Khanaqin, 140 km northeast of Baghdad, in still-violent Diyala province, police said. The all-out sectarian war triggered by the 2003 US invasion has receded in Iraq over the past two years but attacks by suspected insurgents continue. Iraqi and US officials expect attacks to pick up ahead of a March 7 election, a critical juncture as Iraq stands on its own feet ahead of a US withdrawal by end-2011 and signs deals with energy firms that could vault it into the oil big leagues. Khanaqin near the Iranian border is one of many areas where Kurds based in their semi-autonomous northern enclave and the Arab-led government in Baghdad tussle for power.